JP5842911B2 - Piezoelectric device and method for manufacturing piezoelectric device - Google Patents

Description

  The present invention relates to a piezoelectric device using a piezoelectric thin film and a method for manufacturing the piezoelectric device.

  Currently, piezoelectric devices using piezoelectric thin films have been developed. As such a piezoelectric device, for example, Patent Document 1 discloses a surface acoustic wave element.

  FIG. 1A is an external perspective view of the surface acoustic wave device disclosed in Patent Document 1. FIG. FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. The surface acoustic wave element is formed on the surface of the non-piezoelectric substrate 150, the inorganic thin film 140 formed on the surface of the non-piezoelectric substrate 150, the piezoelectric thin plate 120 formed on the surface of the inorganic thin film 140, and the surface of the piezoelectric thin plate 120. Comb-shaped electrodes 130 and 130 '. The inorganic thin film 140 is made of, for example, a silicon oxide film. The material of the piezoelectric thin plate 120 is made of, for example, lithium niobate or lithium tantalate.

  Here, the piezoelectric thin plate 120 made of lithium niobate or lithium tantalate is pyroelectric and highly insulating. Therefore, when manufacturing a piezoelectric device using the piezoelectric thin plate 120 of these materials, the comb-shaped electrodes 130 and 130 ′ formed on the piezoelectric thin plate 120 are destroyed by the pyroelectric charges generated and accumulated in the piezoelectric thin plate 120. There is a problem that it ends up.

  Therefore, conventionally, a reduction process is performed on the piezoelectric thin plate 120 to lower the insulation rate of the piezoelectric thin plate 120, and the pyroelectric charge generated in the piezoelectric thin plate 120 flows out from the piezoelectric thin plate 120 to the non-piezoelectric substrate 150 side. Has been taken.

JP-A-6-326553

However, in a piezoelectric device having a structure in which an inorganic thin film 140 (oxide film) made of a silicon oxide film is formed between a piezoelectric thin plate 120 and a non-piezoelectric substrate 150 formed to be extremely thin with a predetermined thickness (for example, 1 μm) or less, Oxygen is supplied from the inorganic thin film 140 to the piezoelectric thin plate 120. For example, when a piezoelectric device is mounted on a module substrate, heat treatment at 230 ° C. or higher is performed. However, even if the heat treatment is performed in a reflow furnace in a reducing atmosphere, oxygen is supplied from the inorganic thin film 140 to the piezoelectric thin film 120. As a result, the group of 5 to 100 atoms in contact with the oxide film in the piezoelectric thin plate 120 is oxidized, the reduced state of the piezoelectric thin plate is released, and an oxide layer 121 having a high resistivity is formed in the piezoelectric thin plate 120. End up. As a result, as shown in FIG. 2, the pyroelectric charge generated in the piezoelectric thin plate 120 cannot be discharged to the non-piezoelectric substrate 150 side by the oxide layer 121 and is accumulated in the piezoelectric thin plate 120.
Accordingly, in the piezoelectric device having the structure in which the oxide film is formed between the ultrathin piezoelectric thin plate 120 and the non-piezoelectric substrate 150, the comb electrodes 130 and 130 'formed on the piezoelectric thin plate 120 are accumulated in the piezoelectric thin plate 120. There is a problem that it is destroyed by the generated pyroelectric charge. In particular, in a device using an extremely thin piezoelectric body, the influence of the piezoelectric body being oxidized by the oxide film is greater than that in a device using a conventional piezoelectric substrate.

  Accordingly, an object of the present invention is to prevent the ultrathin piezoelectric thin film from being oxidized and prevent the electrodes formed on the piezoelectric thin film from being destroyed by the pyroelectric charge, and the manufacture of the piezoelectric device. It is to provide a method.

  In order to solve the above problems, the piezoelectric device of the present invention has the following configuration.

(1) A piezoelectric device of the present invention includes a support, an oxide film formed on the support, and a piezoelectric thin film formed on a surface of the oxide film facing the support side. The oxide film has a composition ratio with less oxygen than the stoichiometric composition ratio.

This piezoelectric device has a structure in which an oxide film is positioned between a very thin piezoelectric thin film of, for example, 1 μm or less and a supporting substrate. However, in this piezoelectric device, the oxide film has a composition ratio in which oxygen is more deficient than the stoichiometric composition ratio. Therefore, even when heat treatment is performed on the piezoelectric device when the piezoelectric device is mounted on the module substrate, oxygen is hardly supplied from the oxide film to the piezoelectric thin film. Therefore, the piezoelectric thin film is not oxidized, and an oxide layer (see oxide film 121 in FIG. 2) having high resistivity is not formed in the piezoelectric thin film. As a result, pyroelectric charges generated in the piezoelectric thin film flow out to the oxide film.
Therefore, according to this piezoelectric device, it is possible to prevent the ultrathin piezoelectric thin film from being oxidized and to prevent the electrodes formed on the piezoelectric thin film from being destroyed by the pyroelectric charge.

(2) The oxide film is a silicon oxide film,
The composition ratio of the oxide film satisfies the relationship of 1.6 ≦ y / x <2 when it is SixOy.

  According to this composition ratio, oxidation of the piezoelectric thin film can be prevented, and the resistivity of the oxide film itself can be set to a level that does not adversely affect the characteristics of the piezoelectric device.

(3) The resistivity of the piezoelectric thin film is 10 ¹¹ Ω · cm or less.
(4) The piezoelectric thin film is made of a single crystal of lithium niobate or a single crystal of lithium tantalate.

  A piezoelectric thin film made of a single crystal of lithium niobate or a single crystal of lithium tantalate is pyroelectric and highly insulating. Therefore, the piezoelectric device of the present invention is suitable when a piezoelectric thin film made of such a material is used.

  Moreover, the manufacturing method of the piezoelectric device of this invention is equipped with the following structures in order to solve the said subject.

(5) This method for manufacturing a piezoelectric device includes at least an oxide film forming step and a piezoelectric thin film forming step. In the oxide film forming step, an oxide film having a composition ratio with less oxygen than the stoichiometric composition ratio is formed on the support. In the piezoelectric thin film forming step, the piezoelectric thin film is formed on the surface of the oxide film facing the surface on the support side.

The piezoelectric device manufactured by this manufacturing method has a structure in which an oxide film is located between a very thin piezoelectric thin film of, for example, 1 μm or less and a support substrate. However, in this manufacturing method, an oxide film having a composition ratio in which oxygen is more deficient than the stoichiometric composition ratio is formed. Therefore, even when heat treatment is performed on the piezoelectric device when the piezoelectric device is mounted on the module substrate, oxygen is hardly supplied from the oxide film to the piezoelectric thin film. Therefore, the piezoelectric thin film is not oxidized, and an oxide layer (see oxide film 121 in FIG. 2) having high resistivity is not formed in the piezoelectric thin film. As a result, pyroelectric charges generated in the piezoelectric thin film flow out to the oxide film.
Therefore, according to this method of manufacturing a piezoelectric device, the piezoelectric device capable of preventing the ultrathin piezoelectric thin film from being oxidized and preventing the electrodes formed on the piezoelectric thin film from being destroyed by the pyroelectric charge. Can be obtained.

(6) The piezoelectric thin film forming step includes at least an ion implantation step and a separation forming step. In the ion implantation step, an ionized element is implanted into the piezoelectric substrate, thereby forming a portion where the concentration of the element implanted into the piezoelectric substrate reaches a peak. In the separation forming step, separation is performed on the piezoelectric substrate with the portion where the concentration of the implanted element reaches a peak as the separation surface, and a piezoelectric thin film is formed on the surface of the oxide film.

  In a piezoelectric device in which a piezoelectric thin film is formed using an ion implantation process, distortion of the crystal lattice due to ion implantation remains in the piezoelectric thin film, so that the piezoelectric thin film is particularly likely to take up oxygen. Therefore, the method for manufacturing a piezoelectric device of the present invention is suitable for forming a piezoelectric thin film using an ion implantation process.

(7) The oxide film is a silicon oxide film,
The composition ratio of the oxide film satisfies the relationship of 1.6 ≦ y / x <2 when it is SixOy.

  According to this composition ratio, oxidation of the piezoelectric thin film can be prevented, and the resistivity of the oxide film itself can be set to a level that does not adversely affect the characteristics of the piezoelectric device.

(8) The piezoelectric thin film is made of a single crystal of lithium niobate or a single crystal of lithium tantalate.

  A piezoelectric thin film made of a single crystal of lithium niobate or a single crystal of lithium tantalate is pyroelectric and highly insulating. Therefore, the method for manufacturing a piezoelectric device of the present invention is suitable for forming a piezoelectric thin film of such a material.

  According to the present invention, it is possible to prevent the electrodes formed on the piezoelectric thin film from being destroyed by the pyroelectric charge.

FIG. 1A is an external perspective view of the surface acoustic wave device disclosed in Patent Document 1. FIG. FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG. 1 (A) schematically showing the flow of pyroelectric charges in the surface acoustic wave device of Patent Document 1. It is a flowchart which shows the manufacturing method of the piezoelectric device which concerns on embodiment of this invention. FIG. 4 is a cross-sectional view schematically showing a manufacturing process of the piezoelectric device shown in FIG. 3. FIG. 4 is a cross-sectional view schematically showing a manufacturing process of the piezoelectric device shown in FIG. 3. FIG. 4 is a cross-sectional view schematically showing a manufacturing process of the piezoelectric device shown in FIG. 3. FIG. 4 is a cross-sectional view schematically showing a manufacturing process of the piezoelectric device shown in FIG. 3. It is sectional drawing which shows typically the flow of the pyroelectric charge of the piezoelectric device which concerns on embodiment of this invention.

  A method for manufacturing a piezoelectric device according to an embodiment of the present invention will be described with reference to the drawings. In the following description, a method for manufacturing a surface acoustic wave device will be described as an example of a method for manufacturing a piezoelectric device.

  FIG. 3 is a flowchart showing a method for manufacturing a piezoelectric device according to an embodiment of the present invention. 4-7 is sectional drawing which shows typically the manufacturing process of the piezoelectric device which concerns on embodiment of this invention.

  First, as shown in FIG. 4A, a piezoelectric single crystal substrate 1 having a predetermined thickness is prepared. Further, as shown in FIG. 5B described later, a support substrate 50 having a predetermined thickness is prepared. The piezoelectric single crystal substrate 1 uses a lithium tantalate (LT) substrate, and the support substrate 50 uses a glass substrate. At this time, as the support substrate 50, a substrate on which a plurality of piezoelectric devices are arranged is used. Here, in addition to the lithium tantalate substrate, the piezoelectric single crystal substrate 1 may be a lithium niobate substrate, a lithium tetraborate substrate, a langasite substrate, or a potassium niobate substrate. In addition to the glass substrate, the support substrate 50 can be a Si substrate, a quartz substrate, a sapphire substrate, or the like.

Then, as shown in FIG. 4B, hydrogen ions are implanted from the surface 12 side of the piezoelectric single crystal substrate 1 to form an ion implanted portion 100 in the piezoelectric single crystal substrate 1 (FIG. 3: S101). For example, when a lithium tantalate substrate is used as the piezoelectric single crystal substrate 1, hydrogen ions are implanted at a dose of 1.0 × 10 ¹⁷ atoms / cm ² at an acceleration energy of 80 KeV, so that a position about 500 nm deep from the surface 12 is obtained. Thus, a hydrogen distribution portion is formed, and an ion implantation portion 100 is formed. The ion implanted portion 100 is a portion where the concentration of the ion element implanted into the piezoelectric single crystal substrate 1 reaches a peak.
In addition, when materials other than the lithium tantalate substrate are used for the piezoelectric single crystal substrate 1, ion implantation is performed under conditions according to each substrate.

Next, as shown in FIG. 5A, dielectric films 90 and 91 are formed on the surface 12 on the ion implantation portion 100 side of the piezoelectric single crystal substrate 1 (FIG. 3: S102). More specifically, in S102, a silicon oxide film 90 having a thickness of 700 nm is formed on the surface 12 of the piezoelectric single crystal substrate 1 on the ion implantation portion 100 side, and a silicon nitride film 91 having a thickness of 1400 nm is formed on the piezoelectric single film of the dielectric film 90. A film is formed on the surface facing the crystal substrate 1 side. The silicon oxide film 90 and the silicon nitride film 91 are formed by vapor deposition, sputtering, CVD, or the like. At this time, the silicon oxide film 90 and the silicon nitride film 91 need to be insulating films having a resistivity of 10 ⁴ Ω · cm or more. The silicon oxide film 90 acts in a direction to cancel the frequency shift of the piezoelectric thin film 10 made of lithium tantalate when the temperature changes.

  Here, when the composition ratio of silicon atoms to oxygen atoms is 1: 2 which is the stoichiometric composition ratio, the silicon oxide film 90 is the smallest in energy and stable. However, in this embodiment, the film has a composition ratio in which oxygen is more deficient than the stoichiometric composition ratio. Although details will be described later, a silicon oxide film 90 having a composition ratio satisfying the relationship of 1.6 ≦ y / x <2 is formed when SixOy is set.

Next, as shown in FIG. 5B, the support substrate 50 is bonded to the piezoelectric single crystal substrate 1 (FIG. 3: S103). Here, the support substrate 50 corresponds to the “support” of the present invention.
For this bonding, activation bonding called hydrophilic bonding, hydrophilic bonding, or bonding utilizing mutual diffusion through a metal layer can be used. In this embodiment, the support substrate 50 is bonded to the piezoelectric single crystal substrate 1. However, in the implementation, the support substrate 50 may be formed on the piezoelectric single crystal substrate 1 by film formation or the like. .

Next, the joined body of the piezoelectric single crystal substrate 1 and the support substrate 50 shown in FIG. 5B is heated in a vacuum atmosphere (up to 500 ° C. in this embodiment), and separation is performed with the ion implanted portion 100 as a separation surface. (FIG. 3: S104).
Through the separation forming step of S104, a single crystal piezoelectric thin film 10 having a thickness of 500 nm is formed on the support substrate 50 as shown in FIG. In addition, since the silicon oxide film 90 is a film having a composition ratio in which oxygen is more deficient than the stoichiometric composition ratio at the time of heating in the separation forming step of S104, oxygen is not supplied from the silicon oxide film 90 to the piezoelectric thin film 10. The oxidation of the piezoelectric thin film 10 can be prevented.

Next, the surface of the separated piezoelectric thin film 10 is polished and flattened by CMP or the like (FIG. 3: S105). This surface roughness is preferably 0.5 nm or less in terms of arithmetic average roughness Ra.
Next, as shown in FIG. 6A, upper electrodes 60A and 60B and IDT (Interdigital Transducer) electrodes 60C having a predetermined thickness are formed on the surface of the piezoelectric thin film 10 using Al (aluminum) or the like. (FIG. 3: S106).

  The electrodes 60A to 60C may be made of not only Al but also Al, W, Mo, Ta, Hf, Cu, Pt, Ti, Au, etc., alone or in a stacked manner depending on the device specifications. .

  Next, as shown in FIG. 6B, an insulating film 70 is formed on the surfaces of the piezoelectric thin film 10 and the electrodes 60A to 60C in order to protect the piezoelectric thin film 10 and the electrodes 60A to 60C (FIG. 3: S107).

  Next, as shown in FIG. 7A, openings 82A and 82B are formed by etching or the like in the regions where the upper electrodes 60A and 60B of the insulating film 70 are exposed (FIG. 3: S108).

  Next, as shown in FIG. 7B, external terminals are formed (FIG. 3: S109). More specifically, bump pads 61A and 61B are formed on the upper electrodes 60A and 60B, and bumps 62A and 62B are formed on both the bump pads 61A and 61B.

  Finally, packaging using a mold is performed through a dividing process of dividing the plurality of piezoelectric devices 101 formed on the support substrate 50 into individual piezoelectric devices 101. In this way, the piezoelectric device 101 is formed. Therefore, a plurality of piezoelectric devices 101 can be manufactured at once. Therefore, according to this embodiment, since a plurality of piezoelectric devices 101 can be manufactured at once, the manufacturing cost of the piezoelectric devices 101 can be greatly reduced.

As shown in FIG. 7B, the piezoelectric device 101 manufactured by the above manufacturing method has a structure in which the silicon oxide film 90 is located between the piezoelectric thin film 10 and the support substrate 50 which are extremely thin, for example, 1 μm or less. It has become. That is, the piezoelectric thin film 10 and the silicon oxide film are formed so as to be adjacent to each other. Here, in the present embodiment, the silicon oxide film 90 is a film having a composition ratio in which oxygen is more deficient than the stoichiometric composition ratio. Therefore, even when heat treatment is performed on the piezoelectric device 101 when the piezoelectric device 101 is mounted on a module substrate, oxygen is hardly supplied from the silicon oxide film 90 to the piezoelectric thin film 10. Therefore, the piezoelectric thin film 10 is not oxidized, and the oxide layer 121 (see FIG. 2) having a high resistivity cannot be formed in the piezoelectric thin film 10. As a result, as shown in FIG. 8, the pyroelectric charges generated in the piezoelectric thin film 10 flow out to the silicon oxide film 90.
Therefore, according to the piezoelectric device 101 and the manufacturing method thereof of this embodiment, the ultrathin piezoelectric thin film 10 is prevented from being oxidized, and the electrodes 60A to 60C formed on the piezoelectric thin film 10 are destroyed by pyroelectric charges. Can be prevented.

  The piezoelectric thin film 10 made of lithium tantalate has pyroelectricity and high insulation. Therefore, the piezoelectric device 101 of this embodiment and the manufacturing method thereof are suitable for forming the piezoelectric thin film 10 of such a material.

  Further, in the piezoelectric device 101 in which the piezoelectric thin film 10 is formed by using the ion implantation process as in this embodiment, since the distortion of the crystal lattice due to the ion implantation remains in the piezoelectric thin film 10, the piezoelectric thin film 10 is particularly easy to take in oxygen. . Therefore, the piezoelectric device 101 and its manufacturing method of this embodiment are suitable when forming the piezoelectric thin film 10 using an ion implantation process.

  In this embodiment, since the single crystal thin film is formed by ion implantation, bonding, and separation, a thin film having superior piezoelectricity than a polycrystalline thin film formed by sputtering, vapor deposition, CVD, or the like is formed. be able to. In addition, since the crystal orientation of the piezoelectric single crystal substrate 1 is the crystal orientation of the piezoelectric thin film 10, by preparing the piezoelectric single crystal substrate 1 having a crystal orientation corresponding to the characteristics of the piezoelectric device 101, a crystal corresponding to the characteristics can be obtained. A piezoelectric thin film 10 having an orientation can be formed.

  Here, the composition ratio of the silicon oxide film 90 will be described in detail below.

  Table 1 shows that ten samples with different composition ratios of the silicon oxide film 90 were prepared for the piezoelectric device 101 having the structure shown in FIG. 7B, and each sample was heat-treated at 500 ° C. for 30 minutes in a vacuum atmosphere. The experimental results of measuring the resistivity of the piezoelectric thin film 10 and the resistivity of the silicon oxide film 90 are shown.

In order that the piezoelectric thin film 10 made of lithium tantalate does not cause pyroelectric breakdown or the like, the resistivity of the piezoelectric thin film 10 needs to be 10 ¹¹ Ω · cm or less. Therefore, from Table 1, the silicon oxide film 90 needs to have a composition ratio satisfying the relationship of y / x <2 when it is set to SixOy.

The dielectric film needs to have sufficient insulation. When the thickness of the silicon oxide film 90 that is a dielectric film is about 0.1 to 10 μm, the resistivity of the silicon oxide film 90 that does not adversely affect the characteristics of the surface acoustic wave device is 10 ⁶ Ω · cm or more. Is preferred. Therefore, from Table 1, the silicon oxide film 90 needs to have a composition ratio that satisfies the relationship of 1.6 ≦ y / x.

  Therefore, when the thickness of the silicon oxide film 90 is about 0.1 to 10 μm, as the surface acoustic wave device, the silicon oxide film 90 having a composition ratio satisfying the relationship of 1.6 ≦ y / x <2 is formed in the step S102. It is preferable to form a film.

In the above-described embodiment, the dielectric film 90 is a silicon oxide film. However, in the implementation, the dielectric film 90 may be formed of aluminum oxide, tantalum oxide, zinc oxide, or the like. Even in this case, as long as each oxide film has a composition ratio in which oxygen is deficient rather than the stoichiometric composition ratio, the same effects as those of the present embodiment can be obtained. Here, the composition ratio at a level at which the oxidation of the piezoelectric thin film 10 can be suppressed and the resistivity of the oxide film itself does not adversely affect the characteristics of the piezoelectric device is shown below.
The composition ratio of the aluminum oxide film is 1 ≦ y / x <1.5 when AlxOy is set.
The composition ratio of the tantalum oxide film is 2 ≦ y / x <2.5 when TaxOy is set.
The composition ratio of the zinc oxide film is 0.6 ≦ y / x <1, where ZnxOy.

  In the above-described embodiment, the surface acoustic wave device has been described as an example. However, the boundary acoustic wave device, and also a bulk wave device, a gyroscope, an RF switch, a vibration power generation element, etc. The manufacturing method of the present invention can also be applied to various devices.

  Moreover, it should be thought that description of each above-mentioned embodiment is an illustration in all the points, Comprising: It is not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Piezoelectric single crystal substrate 10 Piezoelectric thin film 100 Ion implantation part 101 Piezoelectric device 120 Piezoelectric thin film 121 Oxide layer 130 Comb electrode 140 Inorganic thin film 150 Non-piezoelectric substrate 50 Support substrate 60A, 60B Upper electrode 60C Electrode 61A, B Bump pad 62A, B Bump 70 Insulating film 82A, B Opening 90 Silicon oxide film 91 Silicon nitride film

Claims (7)

A support;
An insulating film formed on the support;
A silicon oxide film formed on the insulating film;
A piezoelectric thin film formed on the silicon oxide film,
The silicon oxide film has a thickness of 0.1 to 10 μm and a resistivity of 10 ⁶ Ωcm or more,
The piezoelectric device satisfying a relationship of 1.6 ≦ y / x <2 when the composition ratio of the silicon oxide film is SixOy.   The piezoelectric device according to claim 1, wherein the insulating film is a silicon nitride film. The piezoelectric device according to claim 1, wherein the piezoelectric thin film has a resistivity of 10 ¹¹ Ω · cm or less.   4. The piezoelectric device according to claim 1, wherein the piezoelectric thin film is made of a single crystal of lithium niobate or a single crystal of lithium tantalate. 5. Forming an ion-implanted portion in the piezoelectric substrate at which the concentration of the element reaches a peak by implanting an ionized element into the piezoelectric substrate;
Forming a silicon oxide film on the surface of the piezoelectric substrate on the ion implantation portion side;
Forming an insulating film on the surface of the silicon oxide film;
Bonding a support to the surface of the insulating film;
Separating the piezoelectric substrate with the ion-implanted portion as a separation surface, and forming a piezoelectric thin film on the surface of the silicon oxide film,
The silicon oxide film has a thickness of 0.1 to 10 μm and a resistivity of 10 ⁶ Ωcm or more,
The method for manufacturing a piezoelectric device, wherein the composition ratio of the silicon oxide film satisfies a relationship of 1.6 ≦ y / x <2, where SixOy is satisfied.   The method for manufacturing a piezoelectric device according to claim 5, wherein the insulating film is a silicon nitride film. The material of the piezoelectric thin film is a single crystal of lithium niobate, or made of a single crystal of lithium tantalate, method for manufacturing a piezoelectric device according to claim 5 or 6.

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